1. Field of the Invention
The present invention relates to a chemical spray system and to a waste liquid tank used in the system. More particularly, it relates to a chemical spray system for supplying a cleansing fluid to a vacuum generator for cleaning the chemical from the generator, and having a waste liquid tank for receiving a mixture of the chemical, cleansing fluid and air.
2. Description of the Related Art
FIG. 1 is a representation showing a conventional chemical spray system of a semiconductor device fabrication facility. As shown in FIG. 1, a developer is sprayed on a wafer 22, rotated by a motor 20, through a nozzle 14 connected to a developer supply tank 18 via a supply pipe 15. The sprayed developer hardens after a certain time, and then the wafer 22 is unloaded and transferred for subsequent processing.
As also shown in FIG. 1, a conventional developer spraying apparatus has an air valve 11 interposed on a suction pipe 10 and operated by a solenoid 12. The suction pipe 10 is in flow (i.e., fluid) communication with the supply pipe 15. A vacuum generator 13 is placed in flow communication with the suction pipe 10 via a sealed waste liquid tank 16. When the generator 13 is operated to evacuate air from the tank 16, the air valve 11 is opened by the solenoid 12, whereby a developer contained at the end of a nozzle 14 is subjected to suction via the suction pipe 10. The suctioned developer is thus introduced into the waste liquid tank 16. This process is controlled by a control part (not shown).
The developer collects at the outlet of the nozzle 14 after the spraying is completed, and resultant drops of the developer fall down onto the wafer 22. The excess developer can cause a malfunction in the next process. To prevent this, after the spray of the developer is completed, the generator 13 is operated, and the resultant vacuum is established in the suction pipe 10 via the sealed waste liquid tank 16 as described above. Therefore, the developer is suctioned from the outlet of the nozzle 14. In addition, developer contained in the nozzle 14 itself and 2 to 3 mm of the supply pipe 15 is suctioned into the tank 16 to prevent later hardening of the developer from clogging the nozzle 14.
Each time the above described operation is repeated, the amount of developer suctioned into the waste liquid tank 16 is increased. Therefore, a level sensor 24 is installed inside the waste liquid tank 16 for detecting the level of the developer, and if the amount of the developer reaches a certain level, the level sensor 24 is activated and an alarm is produced by the control part. An operator then discharges the waste liquid from the full tank 16.
However, the conventional waste liquid discharge scheme suffers a drawback in that the operation of the facility must be halted while the sealed waste liquid tank 16 is detached for manual discharging. In addition, since developer gases are introduced into the generator 13, the inside of the generator 13 becomes corroded, producing sintered material which often clogs the generator 13. Thus the generator malfunctions, resulting in stopping of the whole fabrication process, which in turn decreases the yield of the facility.